1. Technical Field
The present invention relates to a presser foot of a sewing machine which is used for seaming two fabrics while overlapping ends of the two fabrics over a predetermined width, and a sewing machine provided with the presser foot.
2. Description of Related Art
For example, the seaming of a crotch portion of a brief and shorts is executed by using a sewing machine provided with a narrow tubular bed. The seaming is executed in accordance with a procedure of overlapping up and down two fabrics inserted through the tubular bed over a predetermined width from edges of respective ends, feeding them to a needle drop position while pinching them between a needle plate provided in an upper surface of the tubular bed and a presser foot moving down onto the needle plate, and seaming them by a needle moving down to the needle drop position.
In order to execute the seaming properly, it is important to keep the overlapped width of the fabrics to be fed to the needle drop position proper. A sewing machine described in Examined Japanese utility Model Publication No. 59-344577 (1984) is provided with a special presser foot having a knife portion cutting ends of fabrics to be seamed and a guide portion (an upper guide and a lower guide) guiding the fabrics cut by the knife portion and overlapping them up and down.
FIG. 1 is a perspective view showing the vicinity of a needle drop position of a conventional sewing machine provided with the presser foot having the knife portion and guide portion. As shown in FIG. 1, a presser foot 1 is attached to a lower end of a presser bar 10 which is supported by an end portion of a sewing machine arm 2. The presser foot 1 is provided with a presser body 11 fixed to the lower end of the presser bar 10, and two presser legs 12 and 13 continuously provided on a front side of the presser body 11 and extending forward in parallel to each other.
The presser bar 10 is moved down, for example, in accordance with a manual operation. The presser foot 1 moves down in accordance with a downward movement of the presser bar 10, and elastically comes into contact with a needle plate 4 provided on a tubular bed 3. Two fabrics to be seamed (a lower fabric KL and an upper fabric KU) are set in a state where one fabric is pinched between the left presser leg 12 and the needle plate 4, and the other fabric is pinched between the right presser leg 13 and the needle plate 4. The fabrics are fed in a direction shown by an outline arrow in FIG. 1 with an operation of a known feed dog (not shown) repeatedly projecting from the needle plate 4, and are seamed by a plurality of (four in FIG. 1) needles 5, 5, . . . moving down through a needle hole 14 provided approximately in the center of the presser body 11.
Between the left and right presser legs 12 and 13, a guide passage 15 which is open to front ends of the presser legs is formed. In a halfway portion of the guide passage 15, there are arranged a fixed knife 6 which is fixed to the left presser leg 12, and a movable knife 7 which is held by the right presser leg 13 and reciprocates in a lateral direction by a power transmission from an inner portion of the sewing machine arm 2. The lower fabric KL and the upper fabric KU are led to the guide passage 15 in a state where the respective ends are risen and are aligned with each other on the needle plate 4, as illustrated in FIG. 1. The ends of the lower fabric KL and the upper fabric KU reach a position where the fixed knife 6 and the movable knife 7 are arranged, and are cut by a motion of the movable knife 7 which comes into slidable contact with the upper portion of the fixed knife 6 while overlapping with it.
An upper guide 16 is horizontally bridged between the upper surfaces of the left and right presser legs 12 and 13, on the rear sides of the fixed knife 6 and the movable knife 7, and a lower guide 17 (refer to FIGS. 2B and 2C) protruding into the guide passage 15 along the lower surface of the presser leg 12 is provided. The lower fabric KL and the upper fabric KU in which the upper ends are cut by the fixed knife 6 and the movable knife 7 are overlapped up and down according to an undermentioned action of the upper guide 16 and the lower guide 17, and are fed to downward positions (the needle drop positions) of the needles 5, 5, . . . .
FIGS. 2A to 2E are views for explaining a motion of the presser foot 1, and they schematically show cross sections of the presser foot 1 in a direction which is orthogonal to a direction where the lower fabric KL and the upper fabric KU are fed. FIG. 2A shows a cross section in the vicinity of the front end of the presser foot 1, FIG. 2B shows a cross section at positions where the fixed knife 6 and the movable knife 7 are arranged, FIG. 2E shows a cross section at the needle drop position, and FIGS. 2C and 2D show cross sections between the cut position and the needle drop position, respectively.
As shown in FIGS. 2C and 2D, the upper guide 16 has a lower surface which is curved in an arch shape, and is provided in such a manner as to increase its thickness toward a rear side and be continuous with the lower surface of the presser body 11. As shown in FIGS. 2B and 2C, the lower guide 17 is a plate fixed to the lower surface of the presser leg 12, and is provided in such a manner as to increase its length protruding into the guide passage 15 from just after the arrangement positions of the fixed knife 6 and the movable knife 7 toward the rear side.
The lower fabric KL and the upper fabric KU are overlapped over an appropriate width from edges of the respective ends, and are led to the guide passage 15 in a state where the overlapped portions are risen on the needle plate 4, as shown in FIG. 2A. The led lower fabric KL and upper fabric KU reach the slidable contact position between the fixed knife 6 and the movable knife 7, as shown in FIG. 2B, and the ends of the fabrics are cut, and then the fabrics are fed to the rear side as shown in FIGS. 2C and 2D.
During the feeding, the lower fabric KL pressed by the left presser leg 12 is pressed from the left side according to an action of the lower guide 17 protruding into the guide passage 15, and falls along the upper surface of the needle plate 4. The upper fabric KU pressed by the right presser leg 13 is guided by the arch shaped lower surface of the upper guide 16, falls on the lower guide 17, and is overlapped with the upper portion of the lower fabric KL on the needle plate 4 at a terminal end of the lower guide 17. In this state, the lower fabric KL and the upper fabric KU are fed to the needle drop position, and are seamed by the needles 5, 5, . . . moving down to the needle hole 14, as shown in FIG. 2E.
In the sewing machine provided with the presser foot 1 as mentioned above, the lower fabric KL and the upper fabric KU have ends being cut according to the motions of the fixed knife 6 and the movable knife 7, are overlapped up and down according to the actions of the upper guide 16 and the lower guide 17, are fed to the needle drop position, and are seamed in a fixed overlapped width. A worker may appropriately overlap the lower fabric KL and the upper fabric KU, and set the fabrics raised on the needle plate 4 at the front position of the presser foot 1. Accordingly, it is not necessary to finely adjust the overlapped width by a manual operation, and it is possible to seam the fabrics at a high efficiency.
FIGS. 3A to 3C are perspective views showing seams formed by the seaming as seen from a front face side of the fabric. FIG. 3A shows a satisfactory seam. This seam is a mode in which sewing lines formed with four needle threads 50, 50, . . . are lined within a range of the overlapped width on the front faces of the lower fabric KL and the upper fabric KU overlapping from edges of the respective ends over the predetermined width, and a topping thread 51 regularly intertwines with these sewing lines.
In the case of using the above-mentioned presser foot 1, since the lower fabric KL and the upper fabric KU are overlapped, and cut according to the motions of the fixed knife 6 and the movable knife 7, it is possible to set the overlapped width in conformity to the lined width of four needles 5, 5, . . . , and it is possible to form the satisfactory seam shown in FIG. 3A.
However, in the actual sewing, as shown in FIG. 3B, there is a case where the sewing lines on both sides protrude to outer sides of the edges of the lower fabric KL and the upper fabric KU, thereby forming a defective seam. Inversely there is a case where the sewing lines on both sides are positioned in inner sides of the edges of the lower fabric KL and the upper fabric KU away from the edges, thereby forming a defective seam.
In a case where the seam shown in FIG. 3B is formed, only two sewing lines are positioned among four sewing lines made of the needle threads 50, 50, . . . in a portion where the lower fabric KL and the upper fabric KU are overlapped, and there is a problem that a sewing strength comes short. In a case where the seam shown in FIG. 3C is formed, any problem in terms of the strength does not occur, however, in the case where the sewing machine is used for seaming the crotch portion of the brief and the shorts, as mentioned above, the ends of the lower fabric KL and the upper fabric KU which are extra in the outer sides of the sewing lines on both sides come into contact with the skin at a time of wearing the seamed product, and there is a problem that a use feeling is deteriorated.
The inventor of the present application searched about a case example where the defective seam as mentioned above occurs, and found that a cause of the defective seam exists in a kind of the fabric to be seamed.
For example, in the case of sewing a stretchable fabric, the lower fabric KL and the upper fabric KU are cut by the fixed knife 6 and the movable knife 7 in a state where both the fabrics KL and KU are stretched, and the thereafter overlapping is carried out in a state where the lower fabric KL and the upper fabric KU are contracted. In this case, the overlapped width comes short, and the sewing defect as shown in FIG. 3B occurs.
On the contrary, for example, in the case of sewing a soft fabric, the lower fabric KL and the upper fabric KU rise in a state where they are deflected on the needle plate 4, and they are cut by the fixed knife 6 and the movable knife 7 in this state. In this case, the overlapped width of the lower fabric KL and the upper fabric KU becomes too large, and the sewing defect as shown in FIG. 3C occurs.
In order to deal with the above-mentioned problem, there can be considered a way of preparing a plurality of kinds of presser foots 1 in which height positions of the fixed knife 6 and the movable knife 7 are different, and exchanging the presser foot according to the fabrics to be seamed, however, there is a problem that a great deal of work is necessary for exchanging the presser foot, and a working efficiency is lowered.